It is known that biological treatment, for example of water, consists of degrading the organic impurities by the action of a free or fixed purifying biomass containing various microorganisms: bacteria, yeasts, protozoa, metazoa, etc. . . In the free biomass process, by activated sludge, it is impossible to concentrate the various species of microorganisms in large numbers, and it is not very easy to settle if the concentration of the biomass is achieved by settling. The process therefore is limited with regard to the applicable BOD (biological oxygen demand) and COD (chemical oxygen demand) load. In the fixed biomass system, the concentration of biomass (with the bacteria) is performed by hooking onto a support. Aptitude for settling then is no longer a primordial criterion and this technique has a purifying potential quite superior to that of standard processes.
The present invention is in the field of fixed biomass biological purification, advantageously with a fixed granular bed in a biological reactor thus playing a filtration role to retain the excess sludge produced inside the reactor as well as the suspension materials present in the effluent to be treated. The reactor is washed periodically to eliminate the excess sludge and materials in suspension that accumulate.
Of the most high-performance processes, based on this principle of fixed biomass purification, there will be recalled here the process known as "Biocarbone" (registered trademark) developed by the present applicant and which essentially comprises the water to be treated to percolate downward through a submerged, fixed bed of granular filtering material while blowing in an oxygenated gas current at an intermediate level of the bed, under well-determined, critical conditions of water flow, oxygenated gas flow, nature and constitution of the bed, amount of pollution to be eliminated. . . etc. (see, for example, French Pat. Nos. 76.21246 publ. 2 358 362 and 78.30282 publ. 2 439 749; as well as their corresponding foreign patents.